Ultrasonic lead screw motor

ABSTRACT

An apparatus for driving a threaded shaft assembly that contains a threaded shaft with an axis of rotation and, engaged therewith, a threaded nut. Subjecting the threaded nut to ultrasonic vibrations causes the threaded shaft to simultaneously rotate and translate in the axial direction. The threaded shaft is connected to a load that applies an axial force to the threaded shaft.

FIELD OF THE INVENTION

A miniature ultrasonic linear motor assembly comprised of a threadedshaft and, engaged, therewith, a nut.

BACKGROUND OF THE INVENTION

Transducers using piezoelectric electrostrictive, electrostatic, orelectromagnetic technologies are very useful for precise positioning atthe nanometer scale. In the case of a piezoelectric device, the ceramicis formed into a capacitor that changes shape when charged anddischarged creating a force transducer or position actuator. When usedas a position actuator, the shape change of the piezoelectric ceramic isapproximately proportional to the applied voltage. Piezoelectricactuators are limited in range to about 0.1 percent of the length of theceramic which corresponds to typical stroke lengths of tens ofmicrometers. While the high stiffness and nanometer precision ofpiezoelectric actuators is very useful, more stroke is needed for manyapplications.

Numerous piezoelectric motor designs have been developed to “rectify”small ceramic shape changes and generate longer stroke.

A PZT stepping motor is described in U.S. Pat. No. 3,902,084; the entiredisclosure of this United States patent is hereby incorporated byreference into this specification. This motor uses aclamp-extend-clamp-retract operating sequence to add together many shortPZT actuator cycles. This stepping linear actuator operates atfrequencies from DC to several kilohertz, which produces loud noise andvibration. Position is not maintained when power is off. Resolutionbetter than one nanometer is achieved over 200 millimeters of travel.

A PZT inertial stick-slip motor is described in U.S. Pat. No. 5,410,206;the entire disclosure of this United States patent is herebyincorporated by reference into this specification. This motor rotates afine-threaded shaft using a split nut, which forms “jaws” that grip theshaft on opposite sides. A PZT actuator rapidly moves the jaws inopposite directions with an asymmetric alternating current drive signal.Fast jaw movements overcome the clamping friction and create slippage.Slower jaw movements do not slip and rotate the shaft. This stick-slipmotor makes similar noise and vibration as the above stepping motor butmoves 100 times slower and holds position when power is turned off.Resolution better than 50 nanometers is achieved over 25 millimeters oftravel.

Ultrasonic motors use piezoelectric-generated vibrations to createcontinuous movement with high speed, high torque, small size and quietoperation.

One of the earliest ultrasonic piezoelectric motors is described in U.S.Pat. No. 3,176,167; the entire disclosure of this United States patentis hereby incorporated by reference into this specification. Thisunidirectional rotary motor uses a quartz crystal oscillator to move athin rod and drive a ratchet wheel with the objective of driving a clockmechanism.

An example of a standing wave ultrasonic motor is described in U.S. Pat.No. 5,453,653; the entire disclosure of this United States patent ishereby incorporated by reference into this specification. This motoruses a rectangular PZT plate to generate ultrasonic oscillations of acontact point that is preloaded against a moving surface. The electrodepattern on the PZT plate is connected to an alternating current signaland generates two-dimensional oscillations of the contact tip with therequired amplitude and phase to generate a net force against the matingsurface. This ultrasonic motor is quiet and 100 times faster than astepping motor while producing about one third of the force. Generallyultrasonic motors are difficult to stop and start which limitsprecision. An encoder with closed-loop control is typically required toachieve sub-micrometer resolution.

A device for driving a threaded rod using ultrasonic vibrations isdescribed, e.g., in U.S. Pat. No. 6,147,435 of Katsuyuki Fujimura; theentire disclosure of this patent is hereby incorporated by referenceinto this specification. This patent discloses and claims: “. . . Amechanism for driving a screw rod by supersonic vibration, comprising: ascrew rod provided with a groove portion formed helically along an axialdirection thereof; a pair of stands rotatably holding opposite ends ofsaid screw rod; a work rack partially surrounding said screw rod andslidable in the axial direction of said screw rod; at least one firstscrew rod rotation device secured on one side of said work rack andextending from said work rack to said screw rod, said at least one firstscrew rod rotation device comprising a first vibrator contacting withsaid groove portion of said screw rod at a first specific angle, a firstspring urging said first vibrator toward said groove portion of saidscrew rod at a specific pressure and a first piezoelectric actuator forvibrating said first vibrator upon electrical activation to rotate saidscrew rod in a first rotational direction; and at least one second screwrod rotation device secured on another side of said work rack andextending from said work rack to said screw rod, said at least onesecond screw rod rotation device comprising a second vibrator contactingwith said groove portion of said screw rod at a second specific angleopposite said first specific angle, a second spring urging said secondvibrator toward said groove portion of said screw rod at a specificpressure and a second piezoelectric actuator for vibrating said secondvibrator upon electrical activation to rotate said screw rod in a seconddirection.”

The device of U.S. Pat. No. 6,147,435 requires both a “first screw rodrotation device” and a “second screw rod rotation device”; these areillustrated in FIG. 3, e.g., as elements 16 a′ and 16 d′ (which comprisesuch first screw rod rotation device), and as elements 16 b′ and 16 c′(which comprise such second screw rod rotation device.) Referring againto U.S. Pat. No. 6,147,435, when elements 16 a′ and 16 d′ are activatedby ultrasonic vibration, the screw rod 2 is caused to rotate in onedirection; and when elements 16 b′ and 16 c′ are activated by ultrasonicvibration, the screw rod 2 is caused to rotate in the oppositedirection.

The elements 16 a′/16 d′, and 16 b′/16 c′ are never activatedsimultaneously; to do so would waste energy and cause the screw rod 2 toremain stationary.

However, even when such elements 16 a′/16 d′ and 16 b′/16 c′ are notactivated simultaneously, there is a waste of energy. The inactive pairof elements still are contiguous with the threads on screw rod 2 and,thus, cause drag friction.

This drag friction is a problem with the device of U.S. Pat. No.6,147,435. As is described in claim 2 of the patent, and in order tosomewhat solve this problem, with the device of such patent “. . . whenone of said first and second piezoelectric actuators is electricallyactivated, a very small amount of electric current is supplied to theother of said first and second piezoelectric actuators.” The efficiencyof the device of U.S. Pat. No. 6,147,435 is not very high.

It is an object of this invention to provide a mechanism for driving athreaded shaft by ultrasonic vibration that has a substantially higherefficiency than that of U.S. Pat. No. 6,147,435 while providing higherprecision, force, and speed than is typically achieved by otherultrasonic motors of a similar size.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided an apparatus fordriving a threaded shaft assembly comprised of a threaded shaft and,engaged therewith, a nut. The assembly contains means for subjectingsaid nut to ultrasonic vibration and thereby causing said shaft tosimultaneously rotate and translate in the axial direction. The assemblyalso is comprised of means for applying an axial force upon said shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by reference to this specification, theappended claims, and the drawings, wherein like numerals refer to likeelement, and wherein:

FIGS. 1 through 6 show a motor containing four rectangular piezoelectricplates wherein FIG. 1 is a perspective view of such motor, FIG. 2 is anexploded view of such motor, FIG. 3 is an end view of such motor, FIG. 4shows the electrical connections to such motor, FIG. 5 is crosssectional view of motor taken along lines A-A (30) of FIG. 3, FIG. 5Ashows a magnified scale view (47 on FIG. 5) of the thread engagementwith external preload and the motor off, FIG. 5B show the same magnifiedscale view in FIG. 5A with the motor operating, and FIG. 6 is a crosssection view taken along lines B-B (32) of FIG. 3;

FIGS. 7 through 12 illustrate a motor containing four piezoelectricstacks wherein: FIG. 7 is a perspective view of such motor, FIG. 8 is anexploded view of such motor, FIG. 9 is an end view of such motor, FIG.10 shows the electrical connections to such motor, FIG. 11 is crosssection view taken along lines A-A (48) of FIG. 9, and FIG. 12 is crosssection view taken along lines B-B (46) of FIG. 9;

FIGS. 13 through 17 illustrate a motor containing a piezoelectric tubewith four outer electrodes wherein: FIG. 13 is a perspective view ofsuch motor, FIG. 14 is an exploded view of such motor, FIG. 15 is an endview of such motor, FIG. 16 shows the electrical connections to suchmotor, FIG. 17 is cross sectional view taken along lines A-A (56) ofFIG. 15;

FIG. 18 is a schematic illustration of the orbital movement of threadednut for the motor of FIG. 1 showing the rotation and translation of thethreaded shaft;

FIG. 19 is a schematic illustration of the electrical drive signalsrequired to create the movements shown in FIG. 18;

FIG. 20 through 25 show applications of the motor of FIG. 1 packaged andintegrated with linear stages, wherein: FIG. 20 is a perspective view ofthe motor assembly, FIG. 21 is an exploded view of the motor assembly,FIG. 22 is a cross section view of the motor assembly, FIG. 23A is aperspective view of the motor assemble with a reverse view from FIG. 20,FIG. 23B is a perspective view that illustrates of how the motorassembly rotates and translates in the forward direction, FIG. 23C is aperspective view that illustrates how the motor assembly rotates andtranslates in the reverse direction, FIG. 24A shows the motor assemblyintegrated in a linear stage operating in the forward direction, FIG.24B shows the motor assembly integrated in a linear stage operating inthe reverse direction and FIG. 25 shows the motor assembly integrated ina three-axis stage system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment of this invention, a miniature ultrasonic linear motorrotates a lead screw to produce linear movement. A cylinder supports athreaded nut with a first bending mode resonant frequency in theultrasonic range. The cylinder and nut are excited at this resonantfrequency by transducers that cause the nut to orbit at the end of thecylinder. The transducers may be piezoelectric, electrostrictive,electrostatic, electromagnetic or any device that can stimulate theresonant vibration. At least two transducers are required tosimultaneously excite the orthogonal bending modes of the cylinder witha plus or minus 90-degree phase shift and create a circular orbit. Aclose-fitting threaded shaft is installed inside the nut. A resilientaxial load is applied to the shaft through a low friction coupling. Thenut orbits at its resonant frequency, and the shaft's inertia keeps itcentered. The orbit of the nut generates torque that rotates the shaftand creates linear movement. At least two alternating current drivesignals are required for the transducers. The drive frequency mustexcite the mechanical frequency and control phase to achieve a circularnut orbit. Modulation of drive signal amplitude and duration controlvelocity. Phase shift between the drive signals may be positive ornegative, which reverses the direction of the nut orbit and the shaftrotation/translation. This embodiment, and other preferred embodiments,will be described in greater detail in the remainder of thisspecification.

Without wishing to be bound to any particular theory, applicant believesthat the operating principle of one of his ultrasonic linear actuatorsis the excitation of the first bending resonance of a cylindrical tube,which causes one or both ends of the tube to orbit around thecylindrical axis without rotating. In this embodiment, one end of thetube houses a threaded nut that also orbits around a mating threadedshaft and imparts a tangential force via friction thus rotating thethreaded shaft as it orbits. The friction in the threads is helpfulbecause it directly drives the screw. This is in strong contrast toconventional lead screw drives, where the thread contact friction isparasitic and creates windup, backlash and slow response. Anothersignificant advantage of helical threads used in this embodiment is thedirect conversion of rotation to translation with large mechanicaladvantage, which magnifies axial force and reduces linear speed and, asa result, increases precision.

In this embodiment, a transducer both either within or outside of theload path is preferably used to excite the first bending mode. Examplesof transducers that can be used are, e.g., piezoelectric elements andstacks, magnetostrictive materials, and electrostatic materials to namea few. This list does not include all transducer materials, but itshould be understood that any such material or mechanism that could beused to excite the first bending resonance of a cylindrical tube orsimilarly shaped block and achieve the orbit of one or both tube ends isembodied in this patent. The embodiments described herein usepiezoelectric material but could just as easily be embodied with analternate transducer material described above.

Referring to FIGS. 1 through 6, and in the preferred embodiment depictedtherein, an ultrasonic linear motor 10 is depicted. In the embodimentdepicted, four rectangular piezoelectric plates are used to generateultrasonic vibrations. In another embodiment, not shown in FIG. 1, othermeans may be used to generate ultrasonic vibrations.

As used in this specification, the term ultrasonic refers to anoperating frequency in excess of 20,000 Hertz. In one embodiment, theoperating frequency is at least about 25,000 Hertz. In anotherembodiment, the operating frequency is at least about 50,000 Hertz. Inyet another embodiment, the operating frequency is at least about100,000 Hertz.

As used in this specification, the term linear motor refers an actuatorthat produces movement in a substantially straight line by generatingforce and/or displacement. Reference may be had, e.g., to U.S. Pat. No.5,982,075 (ultrasonic linear motor), U.S. Pat. No. 5,134,334 (ultrasoniclinear motor), U.S. Pat. No. 5,036,245 (ultrasonic linear motor), U.S.Pat. No. 4,857,791 (linear motor), and the like. The entire disclosureof each of these United States patents is hereby incorporated byreference into this specification.

Referring again to FIGS. 1 through 6, and in the preferred embodimentdepicted therein, it will be seen that a threaded shaft 12 with aspherical ball tip 26 rotates and produces axial force and motion

The threaded shaft 12 is preferably movably disposed within a housing14. The length 15 of threaded shaft 12 (see FIG. 5) preferably exceedsthe length 13 of housing 14 by at least about 10 millimeters. In oneembodiment, length 15 exceeds length 13 by at least 25 millimeters. Inanother embodiment, length 15 exceeds length 13 by at least 50millimeters.

In one embodiment, the threaded shaft 12 has a first natural frequencythat is less than about 0.2 times as great as the first naturalfrequency of the housing 14. In another embodiment, the first naturalfrequency of the threaded shaft 12 is less than about 0.1 times as greatas the first natural frequency of the housing 14.

As used herein, the term first natural frequency refers to frequency ofthe first normal mode of vibration; see, e.g., page 1253 of theMcGraw-Hill Dictionary of Scientific and Technical Terms, Fourth Edition(McGraw-Hill Book Company, New York, N.Y., 1989. Reference also may behad to pages 5-59 to 5-70 (“Natural Frequencies of Simple Systems) ofEugene A. Avallone et al.'s “Mark's Standard Handbook for MechanicalEngineers” (McGraw-Hill Book Company, New York, N.Y., 1978). Referencealso may be had to U.S. Pat. Nos. 6,125,701, 6,591,608, 6,525,456,6,439,282, 6,170,202, 6,101,840, and the like; the entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

In the embodiment depicted in the Figures, an orbital movement of nut 16is created by the presence of two normal modes of vibration that areacting orthogonal to each other in planes parallel to the axiscenterline (see FIG. 2), as is best illustrated in FIG. 18. These twoorthogonal normal modes of vibration are provided by the interaction ofthe activated transducers (such as, e.g., plates 18, 20, 22, and 24) andthe housing 14; and such interaction causes orbital movement of the nut16 which, in turn, causes rotation and translation of threaded shaft 12.

In one embodiment, the first natural resonance frequency of nut 16 ispreferably at least five times as great as the operating frequency ofmotor assembly 10. It is thus preferred that nut 16 be a substantiallyrigid body.

In one embodiment, the threaded shaft 12 is fabricated from metal thatis substantially stainless steel. In this embodiment, the threaded shaft12 engages with a threaded nut 16 which, is fabricated from metal thatis substantially brass.

As will be apparent, it is preferred to use combinations of materialsfor the threaded shaft 12 and the threaded nut 16 so that abrasion andgalling are minimized. Other combinations of materials that will alsominimize such abrasion and galling may be used in the invention.

Referring again to FIG. 1, it will be seen that threaded shaft 12 iscomprised of a multiplicity of threads 17, preferably in the form of ahelical groove. In one embodiment, the threads 17 have a pitch lowerthan about 250 threads per inch and, preferably, less than about 200threads per inch. In another embodiment, the threads 17 have pitch lowerthan about 100 threads per inch. In one aspect of this embodiment, thethreads 17 have a pitch of from about 40 to about 80 threads per inch.

The threads 17 are preferably engaged with interior threads 19 of nut16, as is best illustrated in FIG. 18. In one preferred embodiment, thepitch of interior threads 19 is substantially equal to the pitch ofexterior threads 17.

Although, for the purposes of simplicity of illustration, the threads 17and 19 are shown totally engaged, (except for FIGS. 5A, 5B and 18) thereis preferably a diametrical clearance between threads 17 and 19 of lessthan about 0.5 times the thread depth 33/35 of threads 17 and/or threads19. This diametrical clearance is best illustrated in FIG. 5A. Means fordetermining this diametrical clearance are well known. Reference may behad, e.g., to U.S. Pat. Nos. 6,145,805, 5,211,101, 4,781,053, 4,277,948,6,257,845, 6,142,749, and the like; the entire disclosure of each ofthese United States patents is hereby incorporated by reference intothis specification. Reference also may be had, e.g., to pages 8-9 etseq. (“Machine Elements”) of the aforementioned “Marks Standard Handbookfor Mechanical Engineers.”

Referring to FIG. 5A, one preferred mode of engagement between threads17 and 19 is illustrated. As will be seen from this Figure, each ofthreads 17 has a tip 29, and each of threads 19 has a tip 31.Additionally, each of threads 17 and 19 has a thread depth, 33 and 35,respectively.

Referring again to FIG. 1, and in the preferred embodiment depictedtherein, it will be seen that rotation of the threaded shaft 12 isproduced by ultrasonic orbits of the threaded nut 16 connected to avibrating housing 14. In the embodiment depicted, the threaded nut 16 ispreferably connected to the housing 14. This is best illustrated in FIG.2.

Referring to FIG. 2, and in the preferred embodiment depicted therein,it will be seen that nut 16 is disposed within orifice 11. The nut 16 issecured within orifice 11 by conventional means such as, e.g., a pressfit, and/or adhesive means, etc.

In the preferred embodiment depicted in FIGS. 1 and 2, nut 16 is acylindrical nut. In another embodiment, not shown, nut 16 is a polygonalnut that may have a square shape, a hexagonal shape, an octagonal shape,etc.

Referring again to FIGS. 1 and 2, and in the preferred embodimentdepicted therein, it will be seen that a multiplicity of ceramic plates18 et seq. are attached to the outside surface 37 of the housing 14.

It is preferred that the ceramic plates 18 et seq. change theirrespective lengths upon being subjected to a electrical voltage and, inparticular, to a change in electrical voltage. As used therein, and asis described elsewhere in this specification, these ceramic plates maybe described as “active ceramic plates.” In one embodiment, the activeceramic plates 18 et seq. are selected from the group consisting ofpiezoelectric plates, electrostrictive plates, and mixtures thereof. Forthe sake of simplicity of discussion, the embodiments of at least FIGS.1 and 2 will be described with reference to piezoelectric plates.

In the embodiment depicted in FIG. 2, four piezoelectric plates 18, 20,22, and 24 are bonded to the outside surface 37 of the housing andgenerate the nut 16 orbital vibrations when excited by alternatingelectrical drive signals on electrodes 21 and 23 on each piezoelectricplate (see FIG. 4).

In one embodiment, only two such piezoelectric plates are used, plates18 and 20. In another embodiment, eight or more piezoelectric plates areused. Regardless of how many such piezoelectric plates are used, asufficient number of such plates are used to excite motion in orthogonalplanes 39 and 41 (see FIG. 2).

For the sake of simplicity of representation, four piezoelectric plates18, 20, 22, and 24 will be discussed. These plates are preferably bondedto the corresponding exterior surfaces 37 of housing 14 so that theplates are completely contiguous with such exterior surfaces 37.

The piezoelectric plates 18 et seq. are connected to a source ofelectrical voltage by electrodes 21 and 23, as is best shown in FIG. 4.As will be apparent, and for the sake of simplicity of representation,the connection of electrodes 21 and 23 is shown only with reference topiezoelectric plate 20, it being understood that comparable connectionsare made with respect to the other piezoelectric plates.

Referring to FIG. 4, and to the preferred embodiment depicted therein,it will be seen that all four inside electrodes 23 are connected toground 25. In this embodiment, the piezoelectric material is a commonlyavailable “hard” composition with low dielectric losses and highdepoling voltage. Thus, for example, one may use a piezoelectricmaterial sold as “PZT-4” by the Morgan Matroc company of Bedsford, Ohio.This preferred material typically has several important properties.

Thus, the preferred material preferably has a dielectric loss factor ofless than about 1 percent at a frequency greater than about 20,000 Hertzand, preferably, less than about 0.5 percent. In one embodiment, thedielectric loss factor is about 0.4 percent at a frequency greater thanabout 20,000 Hertz.

Thus, the preferred material has a d33 piezoelectric charge coefficientof at least about 250 picoCoulomb/Newton's and, preferably, at leastabout 270 picoCoulomb/Newton's. In one embodiment, the preferredmaterial has a d33 piezoelectric charge coefficient of about 285picoCoulomb/Newton's.

Thus, the preferred material has a d31 piezoelectric charge coefficientof at least about—−90 picoCoulomb/Newton's and, more preferably, atleast about −105 picoCoulomb/Newton's. In one embodiment, the d31piezoelectric charge coefficient is about −115 picoCoulomb/Newton's.

In one embodiment, the preferred material is a single crystal materialwith a d33 piezoelectric charge coefficient of at least about 2500picoCoulomb/Newton's, and a d31 piezoelectric charge coefficient of atleast about 900 picoCoulomb/Newton's

For a discussion of some suitable materials, and by way of illustrationand not limitation, reference may be had, e.g., to U.S. Pat. Nos.3,736,532 and 3,582,540. The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification.

By way of further illustration, and as is known to those skilled in theart, low dielectric-loss piezoelectric materials are known to thoseskilled in the art. Reference may be had, e.g., to U.S. Pat. No.5,792,379 (low-loss PZT ceramic composition); the entire disclosure ofthis United States patent is hereby incorporated by reference into thisspecification.

In one embodiment, the piezoelectric material is a single crystalpiezoelectric material. These materials are known in the art. Referencemay be had, e.g., to U.S. Pat. Nos. 5,446,330, 5,739,624, 5,814,917,5,763,983 (single crystal piezoelectric transformer), U.S. Pat. Nos.5,739,626, 5,127,982, and the like. The entire disclosure of each ofthese United States patents is hereby incorporated by reference intothis specification.

Referring again to FIG. 4, and in the preferred embodiment depictedtherein, the axial length of the piezoelectric plates 18, 20, 22, and 24changes in proportion the applied voltage (Vx/86 and Vy/88) and the d₃₁piezoelectric charge coefficient.

As will be apparent, piezoelectric plates 18,22 and 20,24 work togetherin pairs, respectively, to bend the housing 14 (see, e.g., FIGS. 1 and2) and excite the orbital resonance. Alternating electric drive signals86 and 88 are preferably applied to plates 20,24 and 18,22,respectively, with poling directions 43. As is well known to thoseskilled in the art, poling directions 43 are the directions in which thedipoles in the piezoelectric material are aligned during manufacture.Reference may be had, e.g., to U.S. Pat. No. 5,605,659 (method forpoling a ceramic piezoelectric plate), U.S. Pat. No. 5,663,606(apparatus for poling a piezoelectric actuator), U.S. Pat. No. 5,045,747(apparatus for poling a piezoelectric ceramic), and the like. Thedisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

For each plate pair 18,22 and 20,24 the electric field is positive withrespect to the poling direction 43 on one plate and negative withrespect to the poling direction 43 on the opposite plate. Drive signalVx 86 is preferably applied to plates 20,24 and produces simultaneousexpansion on one plate and contraction on the opposite plate and thusbends the housing 14 in the plane 39 (see FIG. 2), and in the Xdirection 72 a/72 b (see FIG. 18). In a similar manner the drive signalVy 88 is applied to plates 18,22 and bends the housing 14 in the plane41 (see FIG. 2), and in the Y direction 74 a/74 b (see FIG. 18).

The housing end 45 opposite the threaded nut 16 preferably supports aguide bushing 28 with a small clearance between the bushing insidediameter and the outside diameter of the threaded shaft 12 (see FIG. 2).The threaded shaft 12 supports a resilient axial force 27 (see FIGS. 5and 6) that is applied via the spherical ball tip 26 using a hard flatsurface that produces low friction.

It is preferred that, during the operation of the motor 10, the axialforce 27 that is preferably transmitted through ball 26 be from about0.1 to about 100 Newton's. As will be apparent, the axial force 27preferably is of similar magnitude to the output driving force. Thespherical ball 26 (see FIG. 2) is one means of coupling threaded shaft12 to its load 27 (see FIG. 5) with low frictional torque. As will beapparent to those skilled in the art, one may use other means forcoupling motion from a rotating threaded shaft to a moving load. Thus,e.g., one may use a rolling element bearing, one may use an arcuate loadcontiguous with a flat surface on threaded shaft 12, etc. Reference maybe had, e.g., to U.S. Pat. No. 5,769,554 (kinematic coupling method),U.S. Pat. No. 6,325,351 (highly damped kinematic coupling for precisioninstruments), etc.; the entire disclosure of each of these United Statespatents is hereby incorporated by reference into this specification.

Referring to FIGS. 1 and 2, the end 45 of the housing 14 opposite thethreaded nut 16 incorporates flanges that are the connection point for astationary cover 58 (FIG. 21). The thread pitch on the shaft 12 and onthe nut 16 converts the orbital tangential force and movement to axialforce and movement. The pitch may be selected to optimize the forcemagnification, speed reduction, resolution enhancement and off-powerholding force.

Referring to FIGS. 7 through 12, and in the preferred embodimentdepicted therein, the ultrasonic linear motor 30 preferably uses fourpiezoelectric stacks 36, 40 and 42 (also see FIGS. 7 and 8) to generateultrasonic vibrations. A threaded shaft 12 with a spherical ball tip 26rotates and produces axial force and motion. The rotation is produced byan ultrasonic orbits of the threaded nut 16 connected to a vibratingcylinder 32. Four piezoelectric stacks 36, 38, 40, and 42 are bonded tothe end of the cylinder opposite the threaded nut and bonded to the basering 34. The four stacks 36 et seq. are constructed using well-knownassembly and electrical interconnection methods 44 with the inside stackleads preferably being connected together to a common ground 35. Theaxial length of the stacks 36 et seq. changes in proportion to theapplied voltage and the d₃₃ piezoelectric charge coefficient. Thepiezoelectric material is a commonly available “hard” composition withlow dielectric losses and high depoling voltage. Alternating electricaldrive signals 86 and 88 are connected to the outside leads of eachpiezoelectric stack 44 and excite orbital vibrations of the nut.Piezoelectric stacks 36 and 40 and 38 and 42 work together in pairs,respectively, to rotate the tube and excite the orbital resonance.Alternating electric drive signals Vx 86 and Vy 88 are applied to stacks38,42 and 36,40, respectively, with poling directions 43. For each stackpair 38,42 and 36,40, the electric field is positive with respect to thepoling direction 43 on one stack and negative with respect to the polingdirection on the opposite stack. Drive signal Vx 86 is applied to stacks38,42 and produces simultaneous expansion on one stack and contractionon the opposite stack; and thus it rotates the tube in the X direction72 a/72 b (see FIG. 18). In a similar manner, the drive signal Vy 88 isapplied to stacks 36,40 and moves the end of the tube in the Y direction74 a/74 b (see FIG. 18). The base ring 34 opposite the threaded nut 16supports a guide bushing 28 with a small clearance between the bushinginside diameter and the outside diameter of the threaded shaft. Thethreaded shaft 12 supports a compliant axial force 27 that is appliedvia the spherical ball tip 26 using a hard flat surface that produceslow friction. The base ring 34 is the connection point for a stationarycover 58 (FIG. 21). The thread pitch on the shaft 12 and nut 16 convertsthe orbital tangential force and movement to axial force and movement.The pitch may be selected to optimize the force magnification, speedreduction, resolution enhancement and off-power holding force.

Referring to FIGS. 13 through 17, the ultrasonic linear motor 50 uses apiezoelectric tube 54 with quadrant electrodes to generate ultrasonicvibrations. A threaded shaft 12 with a spherical ball tip 26 rotates andproduces axial force and motion. The rotation is produced by ultrasonicorbits of the threaded nut 16 connected to a vibrating piezoelectrictube 54. The inside diameter of the tube is a continuous electrode 61,which is grounded 63, and the outside diameter of the tube is dividedinto four separate electrodes 60, 62, 64, and 66. The piezoelectricmaterial is a commonly available “hard” composition with low dielectriclosses and high depoling voltage. The axial length of the portion of thepiezoelectric tube beneath each electrode 60, 62, 64, and 66 changes inproportion the applied voltage and the d₃₁ piezoelectric chargecoefficient. Electrode sections 60,64 and 62,66 work together in pairsrespectively to bend the tube 54 and excite the orbital resonance.Alternating electric drive signals 86 and 88 are applied to plates 60,64and 62,66, respectively, with poling directions 43. For each electrodepair 60,64 and 62,66, the electric field is positive with respect to thepoling direction on one electrode and negative with respect to thepoling direction on the opposite electrode. Drive signal Vx 86 isapplied to electrodes 60,64 and produces simultaneous expansion underone electrode and contraction under the opposite electrode; and thus itbends the tube in the X direction 72 a/72 b (see FIG. 18). In a similarmanner the drive signal Vy 88 is applied to plates 62,66 and bends thetube in the Y direction 74 a/74 b (see FIG. 18).

The tube end opposite the threaded nut 16 is bonded to a base flange 52and holds a guide bushing 28 with a small clearance between the bushinginside diameter and the outside diameter of the threaded shaft. Thethreaded shaft 12 supports a compliant axial force 27 that is appliedvia the spherical ball tip 26 using a hard flat surface that produceslow friction. The base flange is the connection point for a stationarycover 58 (FIG. 21). The thread pitch on the shaft 12 and nut 16 convertsthe orbital tangential force and movement to axial force and movement.The pitch may be selected to optimize the force magnification, speedreduction, resolution enhancement and off-power holding force.

Referring to FIGS. 18 and 19, the motor 10 (see FIG. 1) operation andcorresponding drive signals 86 and 88 used to effect such operation areshown. The piezoelectric plate pairs work together, with one expanding70 while the other simultaneously contracts 69, to bend the housing. Thealternating drive signals Vx 86 and Vy 88 are preferable sinusoidal withequal amplitude 90/91 and a ninety degree phase shift 92 to produce acircular orbit. A positive phase shift 92 produces a positive nut 16orbit direction and a positive shaft 12 rotation 96/translation 98,while a negative phase shift 92 produces a negative orbit direction anda negative shaft rotation/translation. A single orbital cycle of themotor, for one direction of rotation, and the corresponding drive signalamplitudes 90 and 91, are shown sequentially in ninety degree increments76, 78, 80, 82 and 84. The cylindrical bending and orbital movement isshown in the X 72 a/72 b and Y 74 a/74 b directions. The nut contactsthe side of the threaded shaft at one location 73 a with a clearance 73b on the opposite side (see FIG. 5B), whereby the contact impartstangential force and movement that causes the shaft 12 to rotate 96 andtranslate 98 a small amount for each orbital cycle. The amount ofrotation and translation per cycle depends on many factors, includingorbit amplitude, the magnitude of the force 27 acting on the shaft, andthe coefficient of friction and surface finish of the threads. If azero-slip condition is achieved between the contact 73 a of the nut andshaft, the movement per cycle is nominally proportional to thediametrical clearance between the threads. In general, as driveamplitudes 90 and 91 increase, the orbit diameter increases, the normalcontact force between the shaft 12 and nut 16 increases, slippagedecreases, speed increases, and torque/force increases.

The ultrasonic frequency is the inverse of the period (see periods 94 aand 94 b of FIG. 19); and such ultrasonic frequency is preferably thesame for both signals and matches the first bending resonant frequencyof the housing 14.

Referring to FIGS. 20 through 25 the motor assembly 100 is integratesmotor 10 with cover 58 and knurled knob 102. A threaded shaft 112 isdisposed within the motor 10. As is best shown in FIG. 21, the threadedshaft 112 is similar to threaded shaft 12 (see FIG. 1) but differstherefrom in having a smooth spindle 113 integrally attached thereto.The spindle 113 is adapted to be attached to knurled knob 102. Cover 58is attached to motor 10 at flange 45. Knurled knob 102 rotates andtranslates with shaft 112 without contacting cover 58.

FIG. 21 is an exploded view of motor assembly 100. FIG. 22 is asectional view of motor assembly 100.

FIGS. 23A, 23B and 23C illustrate the motor assembly 100. FIG. 23A is aperspective view of motor assembly 100 reversed from FIG. 20. FIG. 23Billustrates operation of motor assembly 100 with the knob 102 and shaft112 rotating clockwise 103 and translating in direction of arrow 105. Bycomparison, FIG. 23C illustrates operation of motor assembly 100 withthe knob 102 and shaft 112 rotating counter clockwise 107 andtranslating in direction of arrow 109.

As will be apparent, and for the sake of simplicity of representation,the physical means of electrical connection to the various components ofthe motor assemblies have been omitted from the Figures.

As will also be apparent, the presence of the knurled knob 102 allowsone to move the motor assembly 100 by manual means instead of or inaddition to moving such motor assembly 100 by electrical means. Thus,e.g., the assembly 100 can be used as a micrometer drive replacementthat will afford a user both the conventional means of manual adjustmentas well as the additional means of electrically automated adjustment.

In one embodiment, not shown, knurled knob 102 is mechanically connectedto an exterior motor to allow for a second means of mechanical movementof the assembly.

FIGS. 24A and 24B illustrate adjustable linear stages 106 that arecomprised of motor assemblies 100 operatively connected to lineartranslation stages 104 a/104 b. In this embodiment cover 58 of motorassembly 100 is attached to the bottom stage portion 104 b and ball 26is in contact with top stage portion 104 a. As will be apparent, whenknurled knob 102 moves in clockwise in direction 103, linear motion inthe direction of arrow 105 is produced. Conversely, when knurled knob102 is move counterclockwise in direction 107, linear motion in thedirection of arrow 109 is produced.

In one embodiment, illustrated schematically in FIGS. 24A and 24B, aspring assembly 111 comprised of pins 115 and 116 (shown in dotted lineoutline) biases translation stage 104 a/104 b in the direction of arrow109. In the embodiment depicted, pin 115 is attached to the top, movablepart 104 a of the assembly, and the pin 116 is attached to thestationary bottom part 104 b of the assembly. As will be apparent, thespring assembly 111 may be used to produce the axial force 27 (see FIGS.5 and 6).

FIG. 25 is a perspective view of a micromanipulator 120 that is capableof moving its stages 106 a, 106 b, and 106 c, in the X, Y, and Z axes.

Although the invention has been described in its preferred form with acertain degree of particularity, it is to be understood that the presentdisclosure of the preferred form can be changed in the details ofconstruction, and that different combinations and arrangements of partsmay be resorted to without departing form the spirit and the scope ofthe invention. In the previous portions of this specification, there hasbeen described an apparatus for driving a threaded shaft assemblycomprised of a threaded shaft with an axis of rotation and, engagedtherewith, a threaded nut, wherein said assembly comprises means forsubjecting said threaded nut to ultrasonic vibrations and therebycausing said shaft to simultaneously rotate and translate in the axialdirection. As will be apparent, one may produce a comparable device thatis comprised of means for causing said threaded shaft assembly tovibrate, thereby causing said threaded nut to simultaneously rotate andtranslate.

1. An apparatus for driving a threaded shaft assembly comprised of athreaded shaft with an axis of rotation and, engaged therewith, athreaded nut, wherein: (a) said assembly comprises means for subjectingsaid threaded nut to ultrasonic vibrations and thereby causing saidthreaded shaft to simultaneously rotate and translate in the axialdirection through said nut, (b) said threaded shaft is operativelyconnected to a load in said axial direction, and (c) said assembly alsois comprised of means for applying an axial force to said threadedshaft.
 2. The apparatus as recited in claim 1, wherein said assemblycomprises means for moving said threaded nut in an orbital direction. 3.The apparatus as recited in claim 1, wherein said threaded nut is asubstantially rigid body.
 4. The apparatus as recited in claim 1,further comprising a housing in which said threaded shaft assembly isdisposed.
 5. The apparatus as recited in claim 4, wherein said threadednut is attached to said housing.
 6. The apparatus as recited in claim 5,wherein said housing has a first bending resonant frequency in excess of20,000 cycles per second, and wherein the first bending mode lies in aplane parallel to said axis of rotation.
 7. The apparatus as recited inclaim 6, wherein said housing has a second bending resonant frequencythat is identical to said first bending resonant frequency, and whereinthe second bending mode lies in a plane orthogonal to said first bendingmode.
 8. The apparatus as recited in claim 6, further comprising meansfor orbiting said threaded nut at a frequency of at least about 20,000orbits per second.
 9. The apparatus as recited in claim 8, furthercomprising means for moving said threaded shaft in a directionsubstantially parallel to said axis of rotation.
 10. The apparatus asrecited in claim 8, further comprising means for rotating said threadedshaft while moving said threaded shaft in a direction substantiallyparallel to said axis of rotation.
 11. The apparatus as recited in claim7 wherein said means for orbiting said threaded nut is comprised of atleast two transducers for changing electrical energy into force.
 12. Theapparatus as recited in claim 11 wherein said transducers are selectedfrom the group consisting of piezoelectric transducers, electrostrictivetransducers, magnetostrictive transducers, electostatic transducers,electromagnetic transducers, and mixtures thereof.
 13. The apparatus asrecited in claim 12 wherein said transducers are piezoelectrictransducers.
 14. The apparatus as recited in claim 13, wherein saidpiezoelectric transducers are piezoelectric plates.
 15. The apparatus asrecited in claim 14, wherein said piezoelectric plates are comprised ofpiezoelectric material with a dielectric loss factor of less than about1 percent at a frequency greater than about 20,000 Hertz.
 16. Theapparatus as recited in claim 14, wherein said piezoelectric plates ofcomprised of piezoelectric material with a dielectric loss factor ofless than about 0.5 percent at a frequency greater than about 20,000Hertz.
 17. The apparatus as recited in claim 1, wherein said threadedshaft is comprised of a multiplicity of threads with a thread pitch offrom about 40 to about 250 threads per inch.
 18. An apparatus fordriving a threaded shaft assembly comprised of a threaded shaft with anaxis of rotation and, engaged therewith, a threaded nut, wherein: (a)said assembly comprises means for subjecting said threaded nut toultrasonic vibrations and thereby causing said threaded shaft tosimultaneously rotate and translate in the axial direction, (b) saidthreaded shaft is operatively connected to a load, and (c) said assemblyalso is comprised of means for applying an axial force to said threadedshaft, wherein said threaded shaft is disposed within a housing, andwherein said threaded shaft is connected to a knob.
 19. The apparatus asrecited in claim 18, further comprising a movable stage connected tosaid threaded shaft and to said housing.
 20. An apparatus comprised ofat least two movable stages that are contiguous with each other, whereineach of said at least two movable stages is comprised of the apparatusof claim
 19. 21. The apparatus as recited in claim 1, wherein saidtranslation in said axial direction through said nut is operativelyconfigured to translate in both a positive axial direction and anegative axial direction.
 22. The apparatus as recited in claim 21,wherein said rotation is operatively configured to rotate in both theclockwise and counterclockwise directions.
 23. An apparatus for drivinga threaded shaft assembly comprised of a threaded shaft with an axis ofrotation and, engaged therewith, a threaded nut, wherein: (a) saidassembly comprises means for subjecting said threaded nut to ultrasonicvibrations and thereby causing said threaded shaft to simultaneouslyrotate and translate in the axial direction through said nut, (b) saidthreaded shaft is operatively connected to a load in said axialdirection, and (c) said assembly also is comprised of means for applyingan axial force to said threaded shaft, and (d) said rotation throughsaid nut occurs through at least 360 degrees.
 24. An apparatus fordriving a threaded shaft assembly comprised of a threaded shaft with anaxis of rotation and, engaged therewith, a threaded nut, wherein: (a)said assembly comprises means for subjecting said threaded nut toultrasonic vibrations and thereby causing said threaded shaft tosimultaneously rotate and translate in the axial direction through saidnut, (b) said threaded shaft is operatively connected to a load in saidaxial direction, and (c) said assembly also is comprised of means forapplying an axial force to said threaded shaft, and (d) said rotationand said translation in said axial direction through said nut occursover a distance greater than the amplitude of any single amplitude ofsaid ultrasonic vibration.